Don't use the spray stuff.
If your last cloth only lasted 9 months with three hours a day of play, it was either cheap cloth or you weren't cleaning it correctly.
Vacuuming after eight hours of play is not too often. That pulls the chalk dust out of the cloth. A brush tends to spread the chalk around and work it into the cloth.
In the old days some table mechanics used plaster of Paris for the seams between the slates and that could crack and get pulled up by the vacuum. I hope your installers used something more permanent. I think a little hand vac is not strong enough for the job.
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This is the best advise.
The very best 3Cushion rooms vacuum after every game no matter how long it takes. 30 Min - 1.5 hours.
On my 3C table I thoroughly vacuum then come back with a very lightly damp micro fiber cloth. Wring evey drop out. Turn it over after each slate. 6X getting around. Cloth is folded in 4ths.
Wipe, Do not Scrub.
Don't forget the rail nose.